Batteries and Metal-Air Batteries
A battery is a device consisting of one or more electrochemical cells convert stored chemical energy into electrical energy. Each cell contains a positive terminal, or cathode, and a negative terminal, or anode. Electrolytes allow ions to move between the electrodes and terminals to generate current, which flows out of the battery to perform work. According to a 2005 estimate, the worldwide battery industry generates US$48 billion in sales each year, with 6% annual growth. A metal-air battery is an electrochemical cell that uses an anode made from pure metal and a cathode utilizing ambient air as terminal electron acceptors, typically with an aqueous electrolyte. The theoretical specific energy densities for metal-air batteries are higher than for ion-based approaches, due to the use of atmospheric oxygen as the cathode, eliminating a traditional cathode structure (non-rechargeable). The common metal-air batteries include aluminum-air, lithium-air, zinc-air, calcium-air, magnesium-air, sodium-air, titaniumair, ion-air batteries. Following Lithium-air and Zinc-air batteries are elucidated as examples.
lithium-air batteries have been proposed as the next step in lithium battery architecture, due to the high specific energy density of lithium with respect to air (3840 mA·h/g)(Kumar 2010). At the cathode, electrons are oxidized by oxygen. Mesoporous carbon has been used as a cathode material with metal catalysts. Metal catalysts incorporated into the carbon electrode enhance the oxygen reduction kinetics and increase the specific capacity of the cathode (Daniel and Besenhard 1999). Manganese, cobalt, ruthenium, platinum, silver, or a mixture of cobalt and manganese are under consideration as metal catalysts. However the metals are expensive and less easy to access. Under some circumstances manganese catalyzed cathodes performed best, with a specific capacity of 3137 mA·H/g carbon, and cobalt catalyzed cathodes performed second best, with a specific capacity of 2414 mA·H/g carbon (Abraham and Jiang 2014).
Li-air cell performance is limited by the efficiency of reaction at the cathode, where most of the cell voltage drop occurs (Kraytsberg 2010). Part of the reason for the undeveloped potential of Li-air cells lays with the lack of a suitable catalyst for effecting the oxygen reduction. Multiple battery chemistries display varying electrochemical reactions at the cathode. The aprotic and aqueous electrolytes as the exact electrochemistry taking place in solid-state electrolytes is not well understood. The performance of li-air battery involves the interface of three phases: liquid electrolyte, solid cathode surface and oxygen gas. The oxygen-cathode interface is thought to be responsible for the rechargeability is the lack of thereof, of lithium-air batteries. Two factors play a crucial role: cathode catalyst composition and cathode porosity.
Li-air batteries are primarily motivated for the application of automotive power supplies because the high specific energy and volumetric energy densities of Li-air battery are the prime motivation for this design. Secondarily, Li-air batteries are attractive for applications demands high power density and light weight carriage, such as mobile devices.
Zinc-air batteries have received attention due to the potential for high energy densities. They are metal-air batteries powered by oxidizing zinc with oxygen from the air. These batteries have high energy densities and are relatively inexpensive to produce. Sizes range from very small button cells for hearing aids, larger batteries used in film cameras that previously used mercury batteries, to very large batteries used for electric vehicle propulsion. Zinc-air batteries can be used to replace now discontinued 1.35 V mercury batteries (although with a significantly shorter operating life), which in the 1970s through 1980s were commonly used in photo cameras. Possible future applications of this battery include its deployment as an electric vehicle battery and as a utility-scale energy storage system. As same as Lithium-air battery, the cathode oxidation reaction rate limits the performance of the zinc-air battery. Treasure metal catalysts are costive and some are causing environmental issues.
Tanaami et al. (U.S. patent application Ser. No. 13/624,938, filed Mar. 16, 2011, and hereby incorporated herein by reference in its entirety and made part of this application) discloses system and design of metal-air battery capable of obtaining large charge-discharge capacity than before. The patent is aiming to solve the problem that at the positive electrode, reaction rate is dominated by a diffusion speed of oxygen molecules and oxygen ions in the oxygen-occluding material. As a result, in the metal air battery equipped with the oxygen-occluding material at the positive electrode, the reaction rate of the battery reaction drops, and over potential increases. The patent try to solve the problem through the oxygen-containing species merely adsorbed at the surface of the mixture of the carbon material and the oxygen-storing material is not necessary to be diffused within the oxygen-storing material. However, the positive electrode, oxygen released from the oxygen occluding material is reduced to form oxygen ions, and form a metal oxide by bonding with the metal ions. Over the time, the metal oxide compounds are accumulated and clog the pore orifices causing termination of the Metal-air battery during discharge process.
In light of the foregoing, there is a need for a cost effective and practical method to solve the issue of the rate retardation of the oxygen oxidation on cathode surface due to slow diffusion of oxygen molecule and lack of catalysis. Also to avoid the accumulation of metal oxide on the electrode surface with high efficiency (90%) for higher efficiency and longer life time of the battery.
The principal object of the present invention is the provision of a process and/or methods for the production of a biological cathode electrode. A still further object of the present invention is the provision of a process of utilizing the biological material in electrode and battery building, especially cathode and metal-air batteries. The biological cathode catalyzes cathode oxygen oxidation reaction without adding expensive treasure metal as catalyst. Using the biological material to replace the caustic battery chemicals is safer and also friendly to environment and human health in long term. Yet another and more particular object of the present invention is the provision of a method, microorganisms, cathode electrode abiotic surface material, composition and apparatus involving biological surface coating cathode to prevent the accumulation of the metal oxide precipitations to enhance the efficiency and prolong the life time of the battery.
Fuel Cells
A fuel cell is a device that converts the chemical energy from a fuel into electricity through a chemical reaction with oxygen or another oxidizing agent (Khurmi 2013). Hydrogen is the most common fuel, but for greater efficiency hydrocarbons can be used directly such as natural gas and alcohols like methanol. Fuel cells are different from batteries in that they require a continuous source of fuel and oxygen/air to sustain the chemical reaction, however, in a battery the chemicals present in the battery react to generate electricity. Fuel cells can continuously produce electricity as long as fuels are supplied.
One example of fuel cell is zinc-air fuel cell. A mass of zinc particles forms a porous anode with an electrolyte. Oxygen in the air is reduced at the cathode and forms hydroxyl ions which migrate to anode, the zinc paste and form zincate, releasing electrons to travel to the cathode through external circuit. The zincate is decayed into zinc oxide and water into the electrolyte after the reaction. The water and hydroxyl from the anode are recycled at the cathode, so the water is not consumed. The reactions produce a theoretical 1.65 volts, but this is reduced to 1.35-1.4 V in available cells. Zinc-air fuel cells: the zinc is the fuel, the reaction rate can be controlled by varying the air flow, and oxidized zinc/electrolyte paste can be replaced with fresh paste.
Tanaami et al. (U.S. patent application Ser. No. 13/624,938, filed Mar. 16, 2011, and hereby incorporated herein by reference in its entirety and made part of this application) discloses system and design of metal-air battery capable of obtaining large charge-discharge capacity than before. The patent is aiming to solve the problem that at the positive electrode, reaction rate is dominated by a diffusion speed of oxygen molecules and oxygen ions in the oxygen-occluding material. As a result, in the metal air battery equipped with the oxygen-occluding material at the positive electrode, the reaction rate of the battery reaction drops, and over potential increases. The patent try to solve the problem through the oxygen-containing species merely adsorbed at the surface of the mixture of the carbon material and the oxygen-storing material is not necessary to be diffused within the oxygen-storing material. However, at the positive electrode, oxygen released from the oxygen containing material is reduced to form oxygen ions, and form a metal oxide by bonding with the metal ions. Over the time, the metal oxide compounds are accumulated and clog the pore orifices causing termination of the Metal-air battery during discharge process.
In light of the foregoing, there is a need for a cost effective and practical method to solve the issue of the rate retardation of the oxygen oxidation on cathode surface due to slow diffusion of oxygen molecule and lack of catalysis. Also to avoid the accumulation of metal oxide on the electrode surface with high efficiency (90%) for higher efficiency and longer life time of the battery.
The principal object of the present invention is the provision of a process and/or microorganism for the production of a biological cathode electrode. A still further object of the present invention is the provision of a process for using microorganisms to catalyze cathode oxygen oxidation reaction without adding expensive treasure metal as catalyst. Yet another and more particular object of the present invention is the provision of a method, microorganisms and apparatus involving biological surface coating cathode to prevent the accumulation of the metal oxide precipitations to enhance the efficiency and prolong the life time of the battery.
Microbial Fuel Cells
Microbial Fuel Cells (MFCs), which can harvest energy from microorganisms in the form of electricity, have gained worldwide interest. MFCs provide an energy alternative in the face of a wide-spread energy crisis and environmental problems. Developing MFC technology has become an urgent requirement for the sake of sustainability of our society. Energy generation in the process of biological oxygen demand (BOD) removal for waste treatment plant is a good example. As well, MFCs can be applied in occasions that battery or other power sources are not feasible, such as powering marine underwater devices etc.
A Microbial Fuel Cell converts chemical energy to electrical energy via electron exchange between two chambers, the anode chamber and the cathode chamber. In the anode chamber, oxygen-starved organic material (for example, wastewater) is oxidized by naturally occurring bacteria. This process releases protons and electrons. Electrons flow through a circuit to the cathode, where they combine with protons and terminal electron acceptors. Oxygen in air is commonly used as terminal electron acceptor for it has high oxidation potential. However the reduction of oxygen is critical and usually the limiting step for power generation. A sluggish oxygen reduction reaction (ORR) causes a large cathodic over-potential, i.e., about 80% of the overall loss in the cell. In previous research of MFC, enhanced performance has been achieved by utilizing specific microbial cultures on the anode side, catalyzing anode reaction and current generation. In particular, it has been shown that an increase in current density can be achieved by isolation of a particular variant of G. sulfurreducens named KN400 (Yi, 2009).
In addition, several other methods to improve the cathode performance include lowering the internal resistance of the cathode material, using more effective electron acceptors such as ferricyanide, potassium permanganate, manganese oxide in place of oxygen, and using a catalyst that efficiently enhances cathodic reactions at room temperature (Yang 2011). Chemical catalysts for the cathode, for example, plain Pt (Reimers, 2001) or Pt-coated carbon (Rozendal 2007) are expensive and only have limited life time (Schamphelaire 2008). Applying noble metals such as platinum in the cathode represents a capital challenge, not only because the substantial increase of the capital costs but also because of the sensitivity of the catalysts to poisoning issues in WC working conditions.
Using microorganisms to catalyze cathode-side reactions has been investigated. However, the performance is limited because of the lack of high-efficiency, functional microorganisms, low microorganism surface interaction with electrode material, medium composition, and other factors. Improved cathode systems and methods for improving cathode-side reactions are needed.
Akasaka et al. (U.S. patent application Ser. No. 12/355,170, filed Jan. 16, 2009, and hereby incorporated herein by reference in its entirety and made part of this application) discloses a pattern-forming material that contains a block copolymer or graft copolymer and forms a structure having micro polymer phases, in which, with respect to at least two polymer chains among polymer chains constituting the block copolymer or graft copolymer, the ratio between N/(Nc-No) values of monomer units constituting respective polymer chains is 1.4 or more, where N represents total number of atoms in the monomer unit, Nc represents the number of carbon atoms in the monomer unit, and No represents the number of oxygen atoms in the monomer unit.
Reppas et al. (U.S. Pat. No. 7,794,969, filed Apr. 13, 2010, and hereby incorporated herein by reference in its entirety and made part of this application) disclose methods and compositions for modifying photoautotrophic organisms as hosts, such that the organisms efficiently convert carbon dioxide and light into n-alkanes, and in particular the use of such organisms for the commercial production of n-alkanes and related molecules.
Ladisch et al. (U.S. patent application Ser. No. 10/875,990, filed Jun. 24, 2004, and hereby incorporated herein by reference in its entirety and made part of this application) disclose a bio-battery that includes a biomolecular energy source in a first electrode cell and a reducible substrate in a second electrode cell, the cells being in ionic communication by a proton exchange membrane.
Evans et al. (U.S. patent application Ser. No. 12/889,155, filed Sep. 23, 2010, and hereby incorporated herein by reference in its entirety and made part of this application) disclose a method of placing a bacterial cellulose matrix in a solution of a metal salt such that the metal salt is reduced to metallic form and the metal precipitates in or on the matrix, and a method for using the metallized bacterial cellulose in the construction of fuel cells and other electronic devices.
Swift et al. (U.S. patent application Ser. No. 12/468,108, filed May 19, 2009, and hereby incorporated herein by reference in its entirety and made part of this application) disclose a microbial fuel cell having multiple, substantially aligned, fibers whose outer surfaces receive a biofilm, the fibers within a conductive tube to form the anode, and the cell further having an anode chamber containing a fluid biomas and a cathode chamber containing an oxygenated fluid.
Han et al. (U.S. patent application Ser. No. 11/534,450, filed Sep. 22, 2006, and hereby incorporated herein by reference in its entirety and made part of this application) disclose a microfluidic device for electrochemically regulating the pH of a fluid comprising: a cathode substrate; an anode substrate facing the cathode substrate and forming a reaction chamber with the cathode substrate; and a nonconductor which forms a boundary between the portions of the cathode substrate and the anode substrate that are capable of contacting one another, wherein at least one of the cathode substrate and the anode substrate is a semiconductor doped with impurities and the other is a metal electrode.
Liu et al. report the use of a conductive and compatible carbon nanotube/chitosan nanocomposite as a new type of MFC biocathode material, fabricated by electrodepositing carbon nanotubes and chitosan onto a carbon paper electrode, which nanocomposite can increase electricity generation and the maximum power density of the MFC with this nanocomposite increase by 67% and 130% (Liu 2011).
Gau (U.S. patent application Ser. No. 12/154,017, filed Jun. 20, 2008, and hereby incorporated herein by reference in its entirety and made part of this application) discloses a biosensor that includes a working electrode, a reference electrode and a counter (auxiliary) electrode, and a method for confining a solution and providing controlled contact between the solutions and electrodes using controllable surface properties and surface tension forces at a small scale, the biosensor capable of sensing ionic macromolecules using a hybridization and enzyme amplification scheme to improve sensitivity.
Ringeisen et al. (Ringeisen 2007) (U.S. patent application Ser. No. 11/978,662, filed Oct. 30, 2007, and hereby incorporated herein by reference in its entirety and made part of this application) disclose a microbial fuel cell comprising a nanoporous membrane having about 100 nm to 1000 nm pore size that sequesters a microbe in the anode chamber, allowing nutrients to flow from the cathode chamber to the anode chamber and modifiable by a thin film composite (TFC) to create a TFC nanofiltration membrane.
Salguero et al. (Salguero 2011) (U.S. patent application Ser. No. 13/326,243, filed Dec. 14, 2011, and hereby incorporated herein by reference in its entirety and made part of this application) disclose a method and apparatus for increasing biofilm formation and power output in microbial fuel cells by incorporating in the anode material a three-dimensional and ordered structure filling the entire anode compartment, allowing fluid flow within the compartment and further allowing a Geobacteraceae biofilm to grow to its natural thickness of about 40 microns.
Lovley et al. (U.S. application Ser. No. 13/514,378, filed Dec. 22, 2010; Pub. No. US 20120288898; and hereby incorporated herein by reference in its entirety and made part of this application), disclose systems and methods for generating organic compounds using carbon dioxide as a source of carbon and electrical current as an energy source, including an embodiment having a reaction cell with a cathode and anode separated by a permeable membrane, the electrodes connected to a source of electrical power, and provided as a film on the cathode a bacterium that can accept electrons and convert carbon dioxide to a carbonbearing compound and water in a cathode half-reaction driven by the application of electrical current from an external source (producing compounds such as acetate, butanol, 2oxobutyrate, proponal, ethanol, and formate).
In light of the foregoing, there is a need for a cost effective and practical method, microorganism, and apparatus for utilizing the above-described sea water or salt water and for producing products, materials, and organic acid salts by other than chemical synthesis of petroleum derived feedstocks.
The principal object of the present invention is the provision of a process and/or microorganism for the production of acetic acid and its salts from carbon dioxide. A still further object of the present invention is the provision of a process for producing acetic acid from saltwater with air or a waste gas stream of CO2 emission from manufactures or industry.
Yet another and more particular object of the present invention is the provision of a method, microorganism and apparatus involving continuous gaseous substrate fermentation under anaerobic conditions to accomplish the conversion of waste gas streams of certain industrial processes into useful products, namely acetic acid and its salts
Acetic Acid Generation
The conventional procedure for producing organic acids and organic acid salts is chemical synthesis of petroleum-derived feedstock. The rapidly escalating cost of petroleum has generated considerable interest in producing these valuable commodities by utilizing renewable or waste material as the feedstock. There is also growing concern over the massive amounts of atmospheric pollutants and greenhouse gases produced by conventional industrial processes. In many cases, CO2 and other gases are discharged directly to the atmosphere, placing a heavy pollution burden on the environment. The global warming issue has captured worldwide attention. Carbon capture technology to reduce global warming problem has become an emerging technology field. In 2011, the U.S. Department of Energy announced a $41 million investment for carbon capture development alone. However, the available techniques are mostly physical and chemical methods, which require tremendous levels of energy.
Acetic acid, a large-volume chemical product, is necessary to produce plastics, synthetic polymers, cloth, detergent, paper, vinegar, and many other important products. The annual production (10 M tons/year) is increasing, owing to high demands in developing countries. The price ($550/ton) is based on global market prices. Producing acetic acid consumes fossil fuels, which are energy-intensive and costly (Seth 2010).
The world's largest producer of virgin acetic acid is the U.S. (2.3 billion pounds in year 2000), accounting for 19% of the total world capacity. Other major contributors are China (44% of global capacity), rest of Asia (21%) and Western Europe (6%). Average growth in global consumption for the period 2009-2014 has been forecasted to be 3-4% annually (IHS, 2013).
Currently, over 80 percent of the U.S. acetic acid is produced by methanol carbonylation. However, this synthetic process requires relatively high temperatures and pressures, exotic materials of construction, and extensive safety-related equipment. The result is a high capital cost. The advantages of producing acetic acid biologically are its appropriateness for small-scale production, lower cost feed stocks, low energy membrane-based purification, and lower temperature and pressure requirements. Potential energy savings by using fermentation methods are estimated to be approximately 14 trillion Btu by 2020 from a reduction in natural gas use. Decreased transportation needs with regional plants will eliminate approximately 200 million gallons of diesel consumption, for combined savings of 45 trillion Btu. If the biological process were to include new acetic acid production, savings could include an additional 5 trillion Btu from production and 7 trillion Btu from transportation energy (Seth 2010).
Conventional Biological Fermentation Production of Acetic Acid
For most of human history, acetic acid was produced by fermentation of sugar to ethyl alcohol and its subsequent oxidation to acetic acid (Raspor and Goranovic 2008).
Genera of the Acetic Acid Bacteria
Acetic acid bacteria (AAB) comprise a large group of aerobic Gram-negative bacteria with the ability to oxidize ethanol to acetic acid (Gram-negative bacteria have an outer membrane that covers a thin sugar-protein (peptidoglycan) shell, which prevents Gram staining; whereas, Grampositive bacteria have a thick layer of peptidoglycan that a Gram stain can penetrate).
They are widely distributed in natural habitats and classified into the family Acetobacteraceae. (Sharafi 2010). These are of the Order: Rhodospirillales and Class: Alpha Proteobacteria. Members of this family are commonly used in industrial production of vinegar. AAB use substrate, such as glucose, ethanol, lactate or glycerol as energy sources. This biological route accounts for only about 10% of world production, owing to the high cost of consumption of food material, occupation of land, etc.; but, it remains important for the production of vinegar, as many food purity laws stipulate that vinegar used in foods must be of biological origin.
Most species of the genera of AAB produce acetic acid through the aerobic route and are within the genus Acetobacter. This genus was first introduced in 1898 with a single species, Acetobacter aceti. The genus Gluconobacter was proposed in 1935 for strains with intense oxidation of glucose to gluconic acid rather than oxidation of ethanol to acetic acid and no oxidation of acetate. The genus “Acetomonas” was described in 1954 for strains with polar flagellation and no oxidation of acetate. Within the AAB, ten genera of the Class Alphaproteobacteria are presently recognized and accommodated to the family Acetobacteraceae. These are: Acetobacter, Gluconobacter, Acidomonas, Gluconacetobacter, Asaia, Kozakia, Swaminathania, Saccharibacter, Neoasaia and Granulibacter. (Yamada 2008)
Anaerobic
Some bacteria that produce acetic acid through the anaerobic route are within the class Clostridia. Species of the genus Clostridium are all Gram-positive and have the ability to form spores. Another prior technology uses anaerobic bacteria to convert carbon monoxide, water (or hydrogen) and carbon dioxide into alcohols, acids and acid salts (See Gaddy et al., European Pat No. 0,909,328 B1, “Biological production of acetic acid from waste gases”, filed Jul. 1, 1996, EP19960922632; Int'l App. No. PCT/US1996/011146; International Pub. No. WO 1998/000558, Sep. 29, 2010 published Sep. 29, 2010, and hereby incorporated herein by reference in its entirety and made part of this application). This method uses waste feedstock as raw material to reduce overall cost. However, it requires strict anaerobic conditions, which demand high operation and maintenance cost. Anaerobic bacteria which are known to convert carbon monoxide and water or hydrogen and carbon dioxide into alcohols and acids and acid salts include Acetobacterium kivui, A. woodii, Clostridium aceticum, Butyribacterium methylotrophicum, C. acetobutylicum, C. formoaceticum, C. kluyveri, C. thermoaceticum, C. thermocellum, C. thermohydrosulfuricum, C. thermosaccharolyticum, Eubacterium limosum, C. ljungdahlii PETC and Peptostreptococcus productus. Anaerobic bacteria known to produce hydrogen from carbon monoxide and water include Rhodospirillum rubrum and Rhodopseudomonas gelatinosa. 
Another prior technology generates organic compounds using carbon dioxide as a source of carbon and electrical current as an energy source (U.S. application Ser. No. 13/514,378, filed Dec. 22, 2010; Pub. No. US 20120288898) as a prior art. Anaerobic microorganisms, Sporomusa ovata (DSM 2662), Sporomusa silvacetica (DSM 10669), Sporomusa sphaeroides (DSM 2875), Clostridium ljungdahlii (DSM 13528), Clostridium aceticum (DSM 1496), Moorella thermoacetica (DSM 21394), Geobacter metallireducens (lab collection, DSMZ 7210) etc were described as functional microorganisms in the system, which require anaerobic working and maintenance conditions, and thus leads to a higher cost.